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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Enhancement of Exciton–Phonon Scattering from Monolayer to Bilayer WS 2

Layered transition metal dichalcogenides exhibit the emergence of a direct bandgap at the monolayer limit along with pronounced excitonic effects. In these materials, interaction with phonons is the dominant mechanism that limits the exciton coherence lifetime. Exciton-phonon interaction also facilitates energy and momentum relaxation, and influences exciton diffusion under most experimental conditions. However, the fundamental changes in the exciton–phonon interaction are not well understood as the material undergoes the transition from a direct to an indirect bandgap semiconductor. Here, we address this question through optical spectroscopy and microscopic theory. In the experiment, we study room-temperature statistics of the exciton line width for a large number of mono- and bilayer WS 2 samples. We observe a systematic increase in the room-temperature line width of the bilayer compared to the monolayer of 50 meV, corresponding to an additional scattering rate of ~0.1 fs –1 . We further address both phonon emission and absorption processes by examining the temperature dependence of the width of the exciton resonances. Using a theoretical approach based on many-body formalism, we are able to explain the experimental results and establish a microscopic framework for exciton–phonon interactions that can be applied to naturally occurring and artificially prepared multilayer structures.

2D materials↗
DOE OSTI2011

Experimental studies on kaonic atoms at DA{Phi}NE

We have measured the K-series x-rays of kaonic hydrogen atoms to determine the strong-interaction energy-level shift and width of the 1s atomic state with significant improvements over the previous experiments. The measurement offers a unique possibility to precisely determine the complex K{sup -}p S-wave scattering length. We have also measured kaonic x-ray spectra with several gaseous targets : deuterium, helium-3 and helium-4. In this paper, we present an overview of this experiment and preliminary spectra of those kaonic x-rays.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Precision spectroscopy of kaonic {sup 3}He X-rays at J-PARC

We will measure the X-rays from kaonic {sup 3}He 3d {yields} 2p transition with a precision below 2 eV. It can provide crucial information on the kaon-nucleus strong interaction. The experiment (J-PARC E17) will be performed as Day-1, which is one of the first experiments in the J-PARC hadron facility in the year 2011. An overview and the present status of the J-PARC E17 experiment are described.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Infrared Constraint on Ultraviolet Theories

While our current paradigm of particle physics, the Standard Model (SM), has been extremely successful at explaining experiments, it is theoretically incomplete and must be embedded into a larger framework. In this thesis, we review the main motivations for theories beyond the SM (BSM) and the ways such theories can be constrained using low energy physics. The hierarchy problem, neutrino mass and the existence of dark matter (DM) are the main reasons why the SM is incomplete . Two of the most plausible theories that may solve the hierarchy problem are the Randall-Sundrum (RS) models and supersymmetry (SUSY). RS models usually suffer from strong flavor constraints, while SUSY models produce extra degrees of freedom that need to be hidden from current experiments. To show the importance of infrared (IR) physics constraints, we discuss the flavor bounds on the anarchic RS model in both the lepton and quark sectors. For SUSY models, we discuss the difficulties in obtaining a phenomenologically allowed gaugino mass, its relation to R-symmetry breaking, and how to build a model that avoids this problem. For the neutrino mass problem, we discuss the idea of generating small neutrino masses using compositeness. By requiring successful leptogenesis and the existence of warm dark matter (WDM), we can set various constraints on the hidden composite sector. Finally, to give an example of model independent bounds from collider experiments, we show how to constrain the DM–SM particle interactions using collider results with an effective coupling description.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

On Baryon-Antibaryon Cross Sections from Initial State Radiation Processes at BABAR and their Surprising Threshold Behavior

BABAR has measured with unprecedented accuracy the e + e - → pp-bar and e + e - → ΛΛ-bar cross sections by means of the initial state radiation technique, which has the advantages of good efficiency and energy resolution, and full angular acceptance in the threshold region. A striking feature of these cross sections is their non-vanishing values at threshold. In the case of charged baryons, the phenomenon is well understood in terms of the Coulomb interaction between the outgoing baryon and antibaryon. However, such an effect is not expected for neutral baryons. We suggest a simple explanation for both charged and neutral baryon pairs based on Coulomb interactions at the valence quark level.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

From dynamical systems to renormalization

In this paper we study logarithmic derivatives associated to derivations on completed graded Lie algebra, as well as the existence of inverses. These logarithmic derivatives, when invertible, generalize the exp-log correspondence between a Lie algebra and its Lie group. Such correspondences occur naturally in the study of dynamical systems when dealing with the linearization of vector fields and the non linearizability of a resonant vector fields corresponds to the non invertibility of a logarithmic derivative and to the existence of normal forms. These concepts, stemming from the theory of dynamical systems, can be rephrased in the abstract setting of Lie algebra and the same difficulties as in perturbative quantum field theory (pQFT) arise here. Surprisingly, one can adopt the same ideas as in pQFT with fruitful results such as new constructions of normal forms with the help of the Birkhoff decomposition. The analogy goes even further (locality of counter terms, choice of a renormalization scheme) and shall lead to more interactions between dynamical systems and quantum field theory.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Assessing compatibility of direct detection data: halo-independent global likelihood analyses

We present two different halo-independent methods to assess the compatibility of several direct dark matter detection data sets for a given dark matter model using a global likelihood consisting of at least one extended likelihood and an arbitrary number of Gaussian or Poisson likelihoods. In the first method we find the global best fit halo function (we prove that it is a unique piecewise constant function with a number of down steps smaller than or equal to a maximum number that we compute) and construct a two-sided pointwise confidence band at any desired confidence level, which can then be compared with those derived from the extended likelihood alone to assess the joint compatibility of the data. In the second method we define a “constrained parameter goodness-of-fit” test statistic, whose p-value we then use to define a “plausibility region” (e.g. where p≥10%). For any halo function not entirely contained within the plausibility region, the level of compatibility of the data is very low (e.g. p<10%). We illustrate these methods by applying them to CDMS-II-Si and SuperCDMS data, assuming dark matter particles with elastic spin-independent isospin-conserving interactions or exothermic spin-independent isospin-violating interactions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

The pp{yields}p{Lambda}K{sup +} and pp{yields}p{Sigma}{sup 0}K{sup +} reactions with chiral dynamics

We report on a theoretical study of the pp{yields}p{Lambda}K{sup +} and pp{yields}p{Sigma}{sup 0}K{sup +} reactions near threshold using a chiral dynamical approach. The production process is described by single-pion and single-kaon exchange. The final state interactions of nucleon-hyperon, K-hyperon, and K-nucleon systems are also taken into account. We show that our model leads to a fair description of the experimental data on the total cross section of the pp{yields}p{Lambda}K{sup +} and pp{yields}p{Sigma}{sup 0}K{sup +} reactions. We find that the experimental observed strong suppression of {Sigma}{sup 0} production compared to {Lambda} production at the same excess energy can be explained. However, ignorance of phases between some amplitudes does not allow one to properly account for the nucleon-hyperon final state interaction for the pp{yields}p{Sigma}{sup 0}K{sup +} reaction. We also demonstrate that the invariant mass distribution and the Dalitz plot provide direct information about the {Lambda} and {Sigma}{sup 0} production mechanisms and may be tested by experiments at COSY or HIRFL-CSR.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Precision Spectroscopy of Kaonic Helium-3 X-rays at J-PARC

We will measure the x-rays from kaonic {sup 3}He and {sup 4}He 3d{yields}2p transition by using silicon drift detectors. Our precision goal is set to 1 eV to provide crucial information on the kaon-nucleus strong interaction in the low energy limit. The experiment is to be performed as one of the first experiment in the J-PARC hadron facility (J-PARC E17). An overview and the present status of the experiment are presented.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Physics at COSY-Juelich

COSY, a storage and cooler synchrotron, which is fed by an injector cyclotron, is operated at Forschungszentrum Juelich (Germany). It provides phase space cooled polarized or unpolarized beams of protons and deuterons with momenta between 0.3 and 3.7 GeV/c for internal experiments and to external target stations. The major experimental facilities, used for the ongoing physics program, are ANKE and WASA (internal) and TOF (external). A new internal target station to investigate polarization build-up by spin-filtering (PAX) has recently been commissioned. COSY is the machine for hadron spin physics on a world-wide scale, which is also used for tests in conjunction with plans to build a dedicated storage ring for electric dipole moment (EDM) measurements of proton, deuteron and {sup 3}He. In this contribution recent results as well as future plans are summarized.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

NONTHERMAL EMISSION FROM MIDDLE-AGED SUPERNOVA REMNANTS INTERACTING WITH MOLECULAR CLOUDS

Supernova remnants (SNRs) interacting with dense molecular clouds (MCs) are proven to be bright {gamma}-ray emitters by recent observations in the GeV-TeV band. We theoretically investigate the multiband radiative properties of the four middle-aged SNRs IC443, W51C, W28, and W44 with a time-dependent injection model. In the model, part of the SNR shell transports into a dense MC, with the other part of the shell evolving in a relatively tenuous interstellar medium. We find a broken power law with a break energy of {approx}3-40 GeV that must be imposed to reproduce the observed multiwavelength spectra for the four remnants. The results indicate that the observed {gamma}-ray spectra can be reproduced as a p-p interaction of the high-energy protons injected by the shell interacting with the MC with the dense matter, whereas the radio emission is produced via synchrotron radiation of the injected electrons from the other part of the shell for the four middle-aged SNRs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

Wakefields generated by collisional neutrinos in neutral-electron-positron plasma

A classical fluid description is adopted to investigate nonlinear interaction between an electron-type neutrino beam and a relativistic collisionless unmagnetized neutral-electron-positron plasma. In this work, we consider the collisions of the neutrinos with neutrals in the plasma and study their effect on the generation of wakefields in this plasma.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Reflection of light beams from a chirped dielectric plane-layered structure

The reflection of light beams with various widths of the angular spectrum from a chirped plane-layered dielectric structure is numerically studied. For wide beams, the total lateral shift of the reflected beam depends on the position of the photonic barrier inside the structure and the value of the Goos – Hänchen shift. For narrow beams, the region of the interaction with the structure increases, the profile broadens and the reflected beam wavefront becomes phase modulated. It is shown that the light reflected from a quasi-periodic structure with negative spatial dispersion undergoes focusing. (light beams)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Role of Tensor Force in Light Nuclei Based on the Tensor Optimized Shell Model

We propose a new theoretical approach to describe nucleus using bare nuclear interaction, in which the tensor and short-range correlations are described with the tensor optimized shell model (TOSM) and the unitary correlation operator method (UCOM), respectively. We show the obtained results of He isotopes using TOSM+UCOM, such as the importance of the pn-pair correlated by the tensor force, and the structure differences in the LS partners of 3/2{sup -} and 1/2{sup -} states of {sup 5}He. We also apply TOSM to the analysis of two-neutron halo nucleus {sup 11}Li, on the basis of the ''core described in TOSM''+n+n model. The halo formation of {sup 11}Li is naturally explained, in which the tensor correlation in the {sup 9}Li core is Pauli-blocked on the p-wave neutrons in {sup 11}Li and the s-wave component of halo structure is enhanced.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Quantum corrections for the cubic Galileon in the covariant language

We present for the first time an explicit exposition of quantum corrections within the cubic Galileon theory including the effect of quantum gravity, in a background- and gauge-invariant manner, employing the field-reparametrisation approach of the covariant effective action at 1-loop. We show that the consideration of gravitational effects in combination with the non-linear derivative structure of the theory reveals new interactions at the perturbative level, which manifest themselves as higher-operators in the associated effective action, which' relevance is controlled by appropriate ratios of the cosmological vacuum and the Galileon mass scale. The significance and concept of the covariant approach in this context is discussed, while all calculations are explicitly presented.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗